WOmi QUANTITIES hlW RELATIONSHIPS 



Use of the series of formulations given in this report is based 

 on the assuKiption that the fisheiy has been stalbilized at two different 

 levels of exploitation during its development, Although the pilchard 

 fishery has never reached complete stability, there were two periods dur- 

 ing its history 'Within which there was little shift in the total catch, 

 and apparently little trend in the total fishiiig effort expended. The 

 first period occurred when the expansion of the industry was temporarily 

 halted by the economic depression of the early thirties and the second 

 included the recent years of the fishery, durjjig which the total catch, 

 after having reached ;j maximiiin in the 1936-37 season, has fluctuated 

 around an annual take of about half a million tons per year. 



Uniform recruitment, as v.-ell as uniform exploitation, are requisites 

 of a stabilized fishery. During the early years of the pilchard fishery, 

 most of the recruitment was furnished 'by unusually successful age groups 

 or broods, which occurred at intervals of about four years. Four "super- 

 abundant groups" have been recognized by Clark (1936) during the 1^ sea- 

 sons, 1919-20 to 1932-33. To average out those fluctuations in recruit- 

 ment, the first period used in the study was chosen to include the passage 

 through the fishery of two of the successful broods (designated groups 

 "C" and "D" by Clark, 1936) and included the fishing seasons 192^^-26 

 through 1932-33} thus representing a time somewhat prior to the depres- 

 sion. During the more recent period (1937-38 through 19Ul-l|2) the dom- 

 inance of unusually successful groups has largely disappeared, (Clark, 

 1939 p. 21) indicating more imiform, recruitment. 



For each of the two levels of exploitation under consideration, it 

 is necessary to have information on: (1) Age composition of the stock a- 

 vailable to the commercial fishery, (2) total catch per season, and (3) 

 relative amounts af effort (product of gear' and tine) expended per season. 

 For the more recent of the two periods, age composition was determined 

 from scales. During the earlier period scale readings were not taken' 

 and it was necessary to deduce age composition from length composition 

 by a method involvirig growth rate and other characteristics of year classes. 

 The total catch records were obtained from the weigh-in reports of the 

 industry and converted to numbers by means of length distributions in 

 samples of the catch in conjunction v/ith previously determined length- 

 weight relationships. Relative amounts of effort were calculated ^y, 

 dividing the total catch by the computed catchrper-unit-of -effort.-' 



Numerical values obtained for the three items of information are 

 given in the accompanying Table 1. The data on age composition are from 

 samples taken in the commorcial fishery throughout each fishing season, 

 exclusive of the summer fishery carried on in the Pacific Northwest. 



-' This computation is in process of revision (19U3). 



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